1 /* 2 * Copyright 2003-2009 Sun Microsystems, Inc. All Rights Reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Sun designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Sun in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, 22 * CA 95054 USA or visit www.sun.com if you need additional information or 23 * have any questions. 24 */ 25 26 package java.lang; 27 28 import java.io.Serializable; 29 import java.io.IOException; 30 import java.io.InvalidObjectException; 31 import java.io.ObjectInputStream; 32 import java.io.ObjectStreamException; 33 34 /** 35 * This is the common base class of all Java language enumeration types. 36 * 37 * More information about enums, including descriptions of the 38 * implicitly declared methods synthesized by the compiler, can be 39 * found in <i>The Java™ Language Specification, Third 40 * Edition</i>, <a 41 * href="http://java.sun.com/docs/books/jls/third_edition/html/classes.html#8.9">§8.9</a>. 42 * 43 * @param <E> The enum type subclass 44 * @author Josh Bloch 45 * @author Neal Gafter 46 * @see Class#getEnumConstants() 47 * @since 1.5 48 */ 49 public abstract class Enum<E extends Enum<E>> 50 implements Comparable<E>, Serializable { 51 /** 52 * The name of this enum constant, as declared in the enum declaration. 53 * Most programmers should use the {@link #toString} method rather than 54 * accessing this field. 55 */ 56 private final String name; 57 58 /** 59 * Returns the name of this enum constant, exactly as declared in its 60 * enum declaration. 61 * 62 * <b>Most programmers should use the {@link #toString} method in 63 * preference to this one, as the toString method may return 64 * a more user-friendly name.</b> This method is designed primarily for 65 * use in specialized situations where correctness depends on getting the 66 * exact name, which will not vary from release to release. 67 * 68 * @return the name of this enum constant 69 */ 70 public final String name() { 71 return name; 72 } 73 74 /** 75 * The ordinal of this enumeration constant (its position 76 * in the enum declaration, where the initial constant is assigned 77 * an ordinal of zero). 78 * 79 * Most programmers will have no use for this field. It is designed 80 * for use by sophisticated enum-based data structures, such as 81 * {@link java.util.EnumSet} and {@link java.util.EnumMap}. 82 */ 83 private final int ordinal; 84 85 /** 86 * Returns the ordinal of this enumeration constant (its position 87 * in its enum declaration, where the initial constant is assigned 88 * an ordinal of zero). 89 * 90 * Most programmers will have no use for this method. It is 91 * designed for use by sophisticated enum-based data structures, such 92 * as {@link java.util.EnumSet} and {@link java.util.EnumMap}. 93 * 94 * @return the ordinal of this enumeration constant 95 */ 96 public final int ordinal() { 97 return ordinal; 98 } 99 100 /** 101 * Sole constructor. Programmers cannot invoke this constructor. 102 * It is for use by code emitted by the compiler in response to 103 * enum type declarations. 104 * 105 * @param name - The name of this enum constant, which is the identifier 106 * used to declare it. 107 * @param ordinal - The ordinal of this enumeration constant (its position 108 * in the enum declaration, where the initial constant is assigned 109 * an ordinal of zero). 110 */ 111 protected Enum(String name, int ordinal) { 112 this.name = name; 113 this.ordinal = ordinal; 114 } 115 116 /** 117 * Returns the name of this enum constant, as contained in the 118 * declaration. This method may be overridden, though it typically 119 * isn't necessary or desirable. An enum type should override this 120 * method when a more "programmer-friendly" string form exists. 121 * 122 * @return the name of this enum constant 123 */ 124 public String toString() { 125 return name; 126 } 127 128 /** 129 * Returns true if the specified object is equal to this 130 * enum constant. 131 * 132 * @param other the object to be compared for equality with this object. 133 * @return true if the specified object is equal to this 134 * enum constant. 135 */ 136 public final boolean equals(Object other) { 137 return this==other; 138 } 139 140 /** 141 * Returns a hash code for this enum constant. 142 * 143 * @return a hash code for this enum constant. 144 */ 145 public final int hashCode() { 146 return super.hashCode(); 147 } 148 149 /** 150 * Throws CloneNotSupportedException. This guarantees that enums 151 * are never cloned, which is necessary to preserve their "singleton" 152 * status. 153 * 154 * @return (never returns) 155 */ 156 protected final Object clone() throws CloneNotSupportedException { 157 throw new CloneNotSupportedException(); 158 } 159 160 /** 161 * Compares this enum with the specified object for order. Returns a 162 * negative integer, zero, or a positive integer as this object is less 163 * than, equal to, or greater than the specified object. 164 * 165 * Enum constants are only comparable to other enum constants of the 166 * same enum type. The natural order implemented by this 167 * method is the order in which the constants are declared. 168 */ 169 public final int compareTo(E o) { 170 Enum other = (Enum)o; 171 Enum self = this; 172 if (self.getClass() != other.getClass() && // optimization 173 self.getDeclaringClass() != other.getDeclaringClass()) 174 throw new ClassCastException(); 175 return self.ordinal - other.ordinal; 176 } 177 178 /** 179 * Returns the Class object corresponding to this enum constant's 180 * enum type. Two enum constants e1 and e2 are of the 181 * same enum type if and only if 182 * e1.getDeclaringClass() == e2.getDeclaringClass(). 183 * (The value returned by this method may differ from the one returned 184 * by the {@link Object#getClass} method for enum constants with 185 * constant-specific class bodies.) 186 * 187 * @return the Class object corresponding to this enum constant's 188 * enum type 189 */ 190 public final Class<E> getDeclaringClass() { 191 Class clazz = getClass(); 192 Class zuper = clazz.getSuperclass(); 193 return (zuper == Enum.class) ? clazz : zuper; 194 } 195 196 /** 197 * Returns the enum constant of the specified enum type with the 198 * specified name. The name must match exactly an identifier used 199 * to declare an enum constant in this type. (Extraneous whitespace 200 * characters are not permitted.) 201 * 202 * <p>Note that for a particular enum type {@code T}, the 203 * implicitly declared {@code public static T valueOf(String)} 204 * method on that enum may be used instead of this method to map 205 * from a name to the corresponding enum constant. All the 206 * constants of an enum type can be obtained by calling the 207 * implicit {@code public static T[] values()} method of that 208 * type. 209 * 210 * @param <T> The enum type whose constant is to be returned 211 * @param enumType the {@code Class} object of the enum type from which 212 * to return a constant 213 * @param name the name of the constant to return 214 * @return the enum constant of the specified enum type with the 215 * specified name 216 * @throws IllegalArgumentException if the specified enum type has 217 * no constant with the specified name, or the specified 218 * class object does not represent an enum type 219 * @throws NullPointerException if {@code enumType} or {@code name} 220 * is null 221 * @since 1.5 222 */ 223 public static <T extends Enum<T>> T valueOf(Class<T> enumType, 224 String name) { 225 T result = enumType.enumConstantDirectory().get(name); 226 if (result != null) 227 return result; 228 if (name == null) 229 throw new NullPointerException("Name is null"); 230 throw new IllegalArgumentException( 231 "No enum constant " + enumType.getCanonicalName() + "." + name); 232 } 233 234 /** 235 * enum classes cannot have finalize methods. 236 */ 237 protected final void finalize() { } 238 239 /** 240 * prevent default deserialization 241 */ 242 private void readObject(ObjectInputStream in) throws IOException, 243 ClassNotFoundException { 244 throw new InvalidObjectException("can't deserialize enum"); 245 } 246 247 private void readObjectNoData() throws ObjectStreamException { 248 throw new InvalidObjectException("can't deserialize enum"); 249 } 250 }